Tucson’s Monsoon 2015 Forecast

The “Super Bowl” of southern Arizona has officially arrived.

For the 6th straight year, I’ve researched the factors that may play a role in the Monsoon. From the eastern Pacific to the ongoing drought across the west, there are many influences on our Summer rainy season. In truth, this is one of the tougher years to call. There’s a lot of positives, but there’s just as many negatives. Let’s delve into my official Monsoon 2015 forecast for Tucson.


Courtesy: Climate Prediction Center
Courtesy: Climate Prediction Center

NOAA’s Climate Prediction Center shows a 33% chance for above normal precipitation mainly east of Tucson between July 1st and September 30th. This includes Cochise, Graham and Greenlee Counties. Meanwhile, odds are equal for above, normal or below average precipitation for Tucson and points west.

While CPC forecasts for Winter periods tend to be fairly accurate, it’s hit or miss during the Monsoon. For more insight on the long range forecast for the Monsoon, I examined the current state of the eastern Pacific Ocean.


Courtesy: IRI
Courtesy: IRI

All signs point to warmer than normal waters in the eastern Pacific ocean, known as El Nino. This was the case last year too, but El Nino never truly developed. In 2015, there is a 95% chance for El Nino conditions during the Monsoon. Pretty much a slam dunk, unlike last year where odds sat at 70%.

El Nino brings a “boom or bust” scenario to the Monsoon. On the plus side, warmer than normal eastern Pacific waters typically leads to an active hurricane season. National Hurricane Center meteorologists are calling for a 70% chance of an above normal season this year. This is already playing out, with Carlos becoming the third named tropical system in the eastern Pacific in less than a month.

In theory, southern Arizona stands a greater than usual chance of seeing remnant moisture from a decaying system or perhaps a tropical depression making it into the desert. History, however, says that’s not always the case.


In a blog post last month, I explained the relationship between the Monsoon and El Nino is a complicated one. Yes, we can see above normal rainfall if we get some type of influence from the eastern Pacific. Yet Monsoon rainfall totals tend to be drier than normal with El Nino, more often than not (AKA: the bust). Since 1951, 10 of the 17 Monsoon Summer with El Nino have led to below normal rainfall in Tucson.

During a typical Monsoon, the eastern Pacific waters are relatively cooler compared to the scorching land temperatures in Mexico. Tick ocean temperatures up a few tenths of a degree and the temperature difference is smaller, thus leading to more stable atmospheric conditions. The net result with El Nino is fewer storms & not as much moisture surging into the state.


Courtesy: US Drought Monitor
Courtesy: US Drought Monitor

There’s a theory the National Weather Service floated in their Monsoon outlook that’s worth mentioning. In the Summer, high pressure generally sets up over the Four Corners. Some research has shown that the placement of the Monsoon high can be dictated by severe drought conditions. Above is the US Drought Monitor valid June 11th. Areas in orange indicate severe drought & potential spots where the high could shift. Notice most of those spots are near the Four Corners and Utah.

This may help keep the pipeline of moisture open to the state. Prolonged periods of winds aloft from the east or southeast could drive enhanced thunderstorm development. It should be noted that this is not a hard and fast rule. Local meteorologists & hydrologists I spoke with say more research is needed.


Courtesy: Sean Parker Photography
Courtesy: Sean Parker Photography

Tucson’s average Monsoon rainfall is 6.08″ Considering the key players over the Summer, I’m expected this year’s version of the Monsoon to be fairly close to that number. History loudly says we should be drier. But the eastern Pacific is a big time wild card. Given the expected active hurricane season off the Mexico coast & early proximity to tropical moisture, respect must be given to these factors when making a long range forecast.



Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s